Snapshot spectral imagers are known. Such imagers perform simultaneous (instantaneous) acquisition of spatial and spectral data in a single snapshot. The data acquired forms a “spectral cube” (also referred to as “data cube”) of a source object (also referred to simply as “object” or “scene”). A spectral cube includes light intensity data in two spatial dimensions and one spectral dimension and is expressed as a three-dimensional (3D) matrix. An advanced SSI system based on a regular digital camera and a 1D disperser inserted in the optical path between an imaged object and the camera sensor chip is disclosed in U.S. Pat. No. 8,081,244, which is incorporated herein by reference in its entirety. Some embodiments disclosed therein further include a blurring element. U.S. Pat. No. 8,081,244 also provides additional background information.
Known snapshot SI designs are based exclusively on computed tomography spectral imaging (CTIS) designs, which use one of two disperser types: a rotating disperser (prism or grating), or a two-dimensional (2D) grating disperser (e.g. in U.S. Pat. Nos. 6,522,403 and 7,092,088). Disadvantages of CTIS imagers include complicated and expensive optical setups with high quality relay optics, some requiring moving parts, the need to process and output huge spectral cubes, an inherent “missing cone” problem in data processing, a lack of miniaturization leading to relatively large sizes, and high cost.
Compressed sensing (CS) based spectral imaging is also known. One CS-SI approach uses a single pixel camera which incorporates a digital micro-mirror array (DMD) driven by pseudo random patterns and a single spectrometer (C. Li et al., IEEE Transactions on Image Processing, Vol. 21(3), pp. 1200-1210, 2012). Other approaches employ variants of “coded aperture snapshot spectral imaging” (CASSI). CASSI uses modulation of an image with a coded aperture and dispersive elements. CASSI variants include a single-shot compressive spectral imager having a dual-disperser architecture (DD CASSI), or a single disperser design (SD CASSI). A more recent approach, referred to as random convolution snapshot spectral imaging (RCSSI), is based on focal plane array measurements of spectrally dispersed coherent sources that have been randomly convoluted by two spatial light modulators. RCSSI requires coherent illumination, which restricts the imaging system considerably.
The known solutions to the problem of acquiring a full spectral cube in a snapshot involve much more complex and expensive hardware that that of a regular digital camera. Moreover, these solutions cannot be miniaturized. There is a therefore a need for, and it would be advantageous to have snapshot spectral imagers based on digital cameras, without any (or with just minimal) hardware changes to the cameras. It would be further advantageous to have such imagers miniaturized.